Various types of information can be obtained from images when identical characteristic points (places) in two images can be associated with each other. For instance, the three-dimensional shape of a subject can be obtained from two images by stereo matching with the use of corresponding characteristic points, which are characteristic points from two images that correspond to each other. Further, a change in a subject can be examined by using corresponding characteristic points to correct images so that subjects of the images overlap. The correction also makes it possible to check whether or not the subjects shot in two images are the same.
Another way to obtain various types of information is to prepare in advance one of characteristic point groups to be compared as three-dimensional data and associate a group of characteristic points extracted from an image or a video with the prepared characteristic point group. This can be utilized in associating, for example, an actually shot satellite image or aerial image with map data. Similarly, this can be utilized in associating an image of a vehicle-mounted camera with car navigation data.
An example of this characteristic point associating method is a graphic form position detecting method described in Patent Literature 1. The method of Patent Literature 1 associates characteristic points from two images that are similar to each other in the arrangement of proximate characteristic points relative to a given characteristic point as corresponding characteristic point candidates, and obtains the distribution of a coordinate alignment parameter for overlapping the corresponding characteristic point candidates. A position where the coordinate alignment parameter is concentrated is used in subsequent processing as a coordinate alignment amount, which is equivalent to an image-to-image conversion parameter.
An image processing device described in Patent Literature 2 creates a set of images of a plurality of resolutions, and associates two images with each other by using a set of different-resolution images created for one image and a set of different-resolution images created for the other image. Images to be compared can thus be associated with each other even when one of the images is enlarged or reduced.
A pattern cross-check device described in Patent Literature 3 estimates a change in shape from the relation between corresponding characteristic point candidates so that graphic forms can be associated with each other despite a change in the shape of the subject.